Individuals with social anxiety disorder (SAD) are an understudied, undertreated sub-group of smokers. Of the 42 million smokers in the United States, an estimated 14.3 million (34%) meet lifetime criteria for SAD. Compared to the general population, individuals with SAD have double the prevalence rates of cigarette smoking (33% vs. 17%), have significantly more unsuccessful quit attempts (64% vs. 49%), and are less likely to remain abstinent after treatment (29% vs. 36%). Despite the evidence that SAD is a significant risk factor for continued smoking and smoking relapse, no known interventions are specifically designed to address the unique needs of this group of smokers. Specifically, the key barriers to successful cessation among this group are: (1) smoking cigarettes to avoid and/or cope with symptoms of social anxiety, and (2) significantly greater levels of craving during times of abstinence. A new, targeted treatment addressing the needs of this significant group of smokers is needed. Web-based Acceptance and Commitment Therapy (ACT) is a new model for delivering smoking cessation treatment that yielded twice the cessation rates as the US government's Smokefree.gov site at 3-month follow-up (23% vs. 10%). Tailoring this intervention to address the unmet needs for smokers with SAD could significantly increase the quit rates of the substantial proportion of smokers with SAD. The proposed treatment development project will tailor an existing web-based ACT intervention for a general population of smokers (WebQuit) into one specifically designed for smokers with SAD (WebQuit-SAD). Development of WebQuit-SAD will be informed by: (1) user receptivity and intervention process data among smokers with SAD who completed the original WebQuit intervention (study in progress; estimated SAD subsample N = 720), (2) focus groups consisting of smokers with SAD, and (3) iterative usability testing. The final product of this project will be an intervention that is technology-enhanced and community-friendly, guided by theory-based mechanisms of change, and with a focus on co-occurring mental health conditions. Thus, it has great potential for broad dissemination and ability to reach and treat the 14.3 million smokers with social anxiety disorder.